The present invention relates to apparatus and to a method of combining high-performance liquid chromatography with capillary gas chromatography. More particularly, the invention is directed to a method and apparatus for on-line coupling of liquid and gas chromatography columns in which there is direct, uninterrupted transfer of sample containing eluent from a liquid chromatographic analytical system to a gas chromatographic system.
In the general area of multidimensional chromatography, the introduction of selected fractions from a liquid chromatographic analytical system into a gas chromatographic system has been described. (K. Grob, Jr., et al., J. Chromatography 295, 55-61 [1984]). However, for the most part, such analyses have been carried out utilizing off-line techniques requiring collection and reinjection of the separate fractions, or by on-line procedures using conventional High Performance Liquid Chromatographic Columns (HPLC), where only a fraction of the separated peak could be introduced into the gas chromatographic equipment.
Efforts to increase the theoretical plate count and the speed of analysis in HPLC have been directed to reducing the particle size of the chromatographic support to a few microns, using open tubular columns analogous to capillary gas chromatography, and reducing column diameter in microbore and, more recently, using packed capillaries.
Among the advantages realized in utilizing packed capillaries for HPLC are the higher total efficiencies obtained by using longer columns, and the reduced eluent consumption. The latter feature permits the use of exotic solvents and the interfacing to detectors such as flame based and mass spectrometers.
The art does describe the use of conventional liquid chromatographic columns which have been coupled to gas chromatographic assemblies. However, the relatively fast flow rates (that is, the large volumes) used permitted only fractions of a peak to be introduced to the gas chromatographic assembly, or only the characterization of well resolved components, for example, one or two peaks in a mixture.
In spite of the widespread interest in conducting sequential, uninterrupted analyses utilizing the combination, in series, of a liquid chromatographic system followed by a gas chromatographic system, no completely satisfactory apparatus or technique has heretofore been achieved. It is, therefore, a principle aim of the present invention to provide an improved apparatus and method whereby the deficiencies and shortcomings of prior art techniques and equipment may be overcome.